Swift初始化中的错误 [英] Errors in Swift initialisers

问题描述

处理在 Swift 中可能失败的 init 的最佳方法是什么？例如，您创建一个依赖于某个可能不可用的资源的类的实例。

What is the best way to handle an init that might fail in Swift? For example, you create an instance of class that depends on a certain resource that might not be available.

显然，我们有两个选项：

Apparently we have 2 options:

• 返回nil的bailable init（Cocoa方式）


• 抛出错误的init

查看下面

enum ThingError: ErrorType{
    case crap
}
class Thing {
    init(c: Int) throws{
        if c < 0 {
            throw ThingError.crap
        }
    }
}



var c = try Thing(c: 3)

do{
    var d = try Thing(c: -4)
}catch{
    print("oh vey!")
}

有没有推荐的方法？第二个选项似乎更多的Swifty...

Is there a recommended way of doing this? The second option seems more "Swifty"...

推荐答案

本质上更好或Swiftier。

Neither is inherently better or Swiftier.

我个人觉得 throws 初始化器是一个巨大的痛苦。我更愿意有一个失败的初始化方法返回 nil ，因为然后我可以用 guard let 必须在 do / catch 中包装内容，并处理结果范围问题。你的代码说明了这个问题;您的 var d 在 do 范围内是stuck。我宁愿这样说：

Personally I find throws initializers a huge pain. I'd much rather have a failed initializer return nil, because then I can do my initialization with guard let instead of having to wrap things in do/catch and deal with the resulting scoping issues. Your code illustrates the problem; your var d is "stuck" inside a do scope. I'd rather say this:

guard let d = Thing(c:-4) else {return}
// now d is unwrapped and in scope!

...比这更好

...than this (what you have to say):

do {
    var d = try Thing(c: -4)
} catch {
    print("oh vey!")
}
// and here there is no `d`, so _now_ what?

另一方面，抛出错误提供了发送消息的机会，即交际关于究竟发生了什么问题。你不能用 init？初始化器来做到这一点;它工作或它失败，这是所有的调用者知道。

On the other hand, throwing an error offers an opportunity to send a message, i.e. to be communicative about exactly what went wrong. You can't do that with a mere init? initializer; it works or it fails, and that's all the caller knows.

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